High In content nitride sub-micrometer platelet arrays for long wavelength optical applications

Abstract

We demonstrate high, up to 30% In content InGaN sub-micrometer platelets on GaN by metalorganic vapor phase epitaxy. These InGaN platelets were selectively grown on flat GaN seeds formed in sub-micrometer-scale openings in a SiNx mask. The platelets were highly uniform without any dislocations or pits, with an atomically flat (0001) surface. The typical height was ∼120 nm, which significantly exceeded the normal critical layer thickness of a c-plane InGaN film. The strain state was comprehensively characterized by microbeam x-ray diffraction and transmission electron microscopy. Due to a gradual elastic relaxation of strain, the In content increased almost linearly from bottom to top because of the strong strain-dependent In incorporation. These platelets can serve as high-quality strain-relaxed templates for long wavelength micro-light-emitting diodes.

Recent Progress in Long‐Wavelength InGaN Light‐Emitting Diodes from the Perspective of Epitaxial Structure

“…Cai et al reported high‐quality and uniform InGaN platelet arrays by selectively depositing InGaN onto submicrometer scale GaN seed arrays by MOVPE. [ 44 ] Such platelets showed a height of 120 nm, where the indium content increased from 15% at the InGaN/GaN interface to about 30% at the atomically flat surface. The obtained high‐quality InGaN pseudosubstrate can serve as high‐quality strain‐relaxed templates for high efficiency, long wavelength optical applications.…”

Red emission from InGaN active layer grown on nanoscale InGaN pseudosubstrates

“…30) We have recently reported on a method to directly fabricate an InGaN platelets array by introducing a flat GaN seed layer before selectively growing InGaN. 31) The use of a low-dislocation-density GaN substrate ensures a homogeneous InGaN platelet array with a flat surface compared with other methods previously reported. 24,25) These InGaN platelets have a high In content of up to 30% and were proved to be dislocation-and pit-free while much strain is relaxed elastically owing to their small size.…”

“…The details of mask patterning before growth and the growth conditions of the GaN seed layer and InGaN platelets have been reported elsewhere. 31) The InGaN platelets were grown at 810 °C, 795 °C and 780 °C to obtain samples with different base In contents, referred to as series 2-4, respectively. For comparison, platelets were also grown without feeding trimethylindium (TMI), which led to pure GaN platelets, referred to as series 1.…”

“…The pits were near the edges of the hexagonal c-plane surface, which had the highest In content in the platelet structure. 31) Additionally, In atoms diffusing from the mask and the vapor phase also gathered at the corner, resulting in the formation of pits, which might be related to local slips similar to InGaN-film-related trench defects. 32,33) Room-temperature CL spectra were sampled in the spot mode at the center of a single platelet for each series from 1 to 4.…”

“…The In distribution presented by CL measurement is consistent with the results of our previously reported elemental mapping. 31) The CL spectrum of the nanoplatelets with red-emitting InGaN active layer (series 4b) has two distinct peaks. The peak around 535 nm is similar to series 4a, which is the base platelet.…”